The present invention relates to molten metal pouring with a retractable shield for improved control of the flow of molten metal into a mold during a casting process, particularly when mold components or equipment are exposed to abnormal flow of molten metal.
Generally the art of metal casting can be described as the pouring of molten metal from a vessel, such as a tundish, into the gating system of a mold to fill cavities that represent the articles to be cast. In an automated casting line, molds are consecutively placed (indexed) with the gating system under the nozzle of the tundish, and a normal flow of molten metal flows through the nozzle into the gating system. Between normal filing of consecutive molds, the normal flow of molten metal is blocked by a stopper placed over the opening in the nozzle as the filled mold is replaced by a fresh mold in the indexed position underneath the nozzle. While the stopper generally prevents the flow of molten metal during this xe2x80x9cdwell timexe2x80x9d period, abnormal flows of molten metal, such as drippings or irregular flows from a leaking nozzle, will sometimes occur during the dwell time.
In one type of casting process, known as the xe2x80x9cLost Foamxe2x80x9d casting process, a foam (typically a low density organic compound) cluster of connected patterns comprising a foam gating system and foam patterns of the articles to be cast is embedded in sand within a mold container. Molten metal is poured onto the top of the foam gating system and evaporates the foam as it progresses through the gating system and into the interconnected foam patterns that represent the articles to be cast. In a properly executed lost foam casting process, the metal replaces the entire cluster of foam patterns to exactly duplicate all of the features of the original patterns.
The lost foam process requires that the flow of molten metal be smooth and quickly executed onto the gating system foam and through the foam patterns as it displaces the evaporated foam. An abnormal flow pattern, such as the discontinuous dripping or trickling of molten metal from the flow nozzle between termination of a pour for a first mold and the beginning of a pour for a second mold, can result in deformed castings being formed in the second mold. One known solution is to protect the top of the foam gating system with a sheet of aluminum foil. The sheet will generally repel non-continuous molten metal droplets but will not protect the foam when the abnormal flow pattern is more continuous when, for example, the nozzle leaks a stream of molten metal. An alternative known solution is to blow away molten metal droplets before they reach the top of the foam gating system by using what is known as an air knife. The air knife requires a compressed air source, produces a loud sound from the release of the compressed air, and propels molten metal droplets in a manner that can be a safety hazard.
Therefore, there exists the need for a simple and efficient apparatus and method for shielding the top of a foam gating system by diverting abnormal flow patterns of molten metal from the top of the foam gating system.
In its broadest aspect, the present invention is an apparatus and a method for pouring molten metal from a vessel onto the gating system of a mold. A nozzle in the vessel directs flow of the molten metal from the vessel onto the gating system. A stopper is used to control the flow of molten metal through the nozzle. A retractable shield is placed between the outlet of the nozzle and the top of the gating system of the mold to divert abnormal flow from the nozzle from the top of the gating system.
These and other aspects of the invention will be apparent from the following description.